Double-bridge Hybrid DC Breaker Topology And Its Control Scheme Research

Compared with AC power transmission,HVDC power transmission has many advantages,such as low line loss and no system synchronization stability.With the rapid development of multi-end flexible DC transmission and distribution technology and high-voltage voltage source converter technology in recent years,DC circuit breakers are playing an increasingly important role in the DC grid.In the event of a fault,the DC circuit breaker needs to complete the action within the specified time and remove the fault to limit the short circuit current.Therefore,the DC circuit breaker is an indispensable basic equipment for the development of the future DC grid.At present,the research and development of high-voltage DC circuit breakers are mainly restricted by the following points: In DC transmission,there is no natural zero-crossing point in the DC current,which results in the arc not easily extinguished during the opening process;after the DC current is opened,the system will generate The voltage phenomenon can easily lead to the component being burned out.At the same time,during the removal of the fault current,a large amount of energy stored in the system needs to be absorbed by the discharge.Compared to the AC system,the DC system impedance is very small(in the steady state,only the resistance).Therefore,the short circuit current rises rapidly.This requires the DC circuit breaker to accurately cut the fault within milliseconds and remove the fault.The current research and development of DC circuit breakers include mechanical DC circuit breakers,all-solid-state DC circuit breakers,and hybrid DC circuit breakers.Firstly,this article describes the current development of DC circuit breakers in domestic and foreign,and studies and summarizes new DC circuit breakers currently under study.The current problems of DC circuit breakers are pointed out.In view of the shortcomings of the existing hybrid DC circuit breakers,this paper presents a new type of DC circuit breaker topology scheme and control strategy.Secondly,a detailed analysis and comparison of the hybrid energy HVDC circuit breaker proposed by ABB and the energy absorption characteristics of the new DC circuit breaker proposed in this paper are introduced.The internal control principle of the hybrid DC circuit breaker is introduced and deduced.Out of its action criteria.The outstanding feature of this new type of DC circuit breaker topology is that a hybrid structure of a mechanical switch and a solid state switch is used.While retaining the good static characteristics of the mechanical switch and the good dynamic characteristics of the solid state switch,the rated voltage and the energy consumption capacity of the DC arrester is greatly reduced.Thereby reducing the manufacturing cost of the circuit breaker;at the same time,the program further increases the current cut-off speed of the hybrid DC circuit breaker;due to the addition of the auxiliary circuit,the life of the circuit breaker is extended by realizing the Zero Voltage Switch(ZVS)of the solid state switch group at closing.Based on the said theory,combined with the action criteria of the hybrid DC circuit breaker,a 320kV/640 MW DC circuit breaker simulation model was built in the power system simulation software,and compared the simulation results with the structure proposed by ABB in November 2012 to verify the superiority of the program.Furthermore,a hardware experiment device under low-voltage(50V)low-current conditions was built in the laboratory,which verified the theoretical correctness and feasibility of the practical application.